Horton

Re: Support to define custom wait events for extensions

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Michael Paquier <michael@paquier.xyz>
Cc: Masahiro Ikeda <ikedamsh@oss.nttdata.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Tristan Partin <tristan@neon.tech>, pgsql-hackers@lists.postgresql.org
Date: 2023-08-08T22:59:54Z
Lists: pgsql-hackers 
Hi,

On 2023-08-08 08:54:10 +0900, Michael Paquier wrote:
> - WaitEventExtensionShmemInit() should gain a dshash_create(), to make
> sure that the shared table is around, and we are going to have a
> reference to it in WaitEventExtensionCounterData, saved from
> dshash_get_hash_table_handle().

I'm not even sure it's worth using dshash here. Why don't we just create a
decently sized dynahash (say 128 enties) in shared memory? We overallocate
shared memory by enough that there's a lot of headroom for further entries, in
the rare cases they're needed.

> We are going to need a fixed size for these custom strings, but perhaps a
> hard limit of 256 characters for each entry of the hash table is more than
> enough for most users?

I'd just use NAMEDATALEN.

- Andres

Commits

  1. Change custom wait events to use dynamic shared hash tables

  2. Support custom wait events for wait event type "Extension"

  3. Add WAIT_EVENT_{CLASS,ID}_MASK in wait_event.c

  4. worker_spi: Switch to TAP tests

  5. Simplify some conditions related to [LW]Lock in generate-wait_event_types.pl